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Abstract:

An antenna pointing system for selectively moving a payload relative to a
mounting surface includes at least one rotary actuator having a moving
part movable relative to a fixed part mounted on the surface. A
connecting rod movably connects to the moving part and to the payload. A
flexible mounting structure movably attaches the payload to the mounting
surface.

Claims:

1. An antenna pointing system for selectively moving a payload relative
to a mounting surface, said system comprising: at least one rotary
actuator having a moving part being movable relative to a fixed part
adapted for mounting on the surface; a connecting rod movably connecting
to the moving part at a first end thereof and adapted for movably
connecting to the payload at a second end thereof; and a flexible
mounting structure for movably attaching the payload to the mounting
surface.

2. The antenna pointing system of claim 1, wherein the at least one
rotary actuator includes first and second rotary actuators connecting to
respective said connecting rod with said second ends of said connecting
rods movably connecting to corresponding first and second attachment
points of the payload.

3. The antenna pointing system of claim 2, wherein the first and second
attachment points are angularly spaced from one another relative to a
rotation center of the flexible mounting structure.

4. The antenna pointing system of claim 3, wherein the first and second
attachment points are substantially adjacent a perimeter of the payload.

5. The antenna pointing system of claim 2, wherein the first and second
attachment points are substantially 90 degrees apart from one another
relative to the rotation center of the flexible mounting structure.

6. The antenna pointing system of claim 1, wherein the flexible mounting
structure is located adjacent a geometric center of the payload.

7. The antenna pointing system of claim 1, wherein the flexible mounting
structure is a universal joint structure.

Description:

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority of U.S. Provisional Application
for Patent No. 61/630,985 filed Dec. 23, 2011, the content of which is
incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

[0002] The present invention relates to the field of antenna systems, and
is more particularly concerned with pointing systems for steerable
antennas.

BACKGROUND OF THE INVENTION

[0003] It is well known in the art to use steerable (or tracking) antennas
to communicate with a relatively moving target over a scan angle.
Especially in the aerospace industry when the antenna is on board of a
spacecraft, such steerable RF (Radio Frequency signal) antennas
preferably need to have precise pointing, high gain, low mass, and high
reliability.

[0004] Satellites often contain two (2) degree of freedom pointing devices
to communicate, sense, etc. with other satellites or bodies. Since the
distances are large, the pointing accuracy and resolution is critical.

[0005] The payload of these pointing devices is variable. Some payloads
are full antennas, portions of an antenna, sensors, etc.

[0006] Many different pointing devices have been devised in the past. The
simplest one being two rotary actuators (RA) assembled in a sequential
chain and holding the payload, such as a reflector, as shown in FIGS. 1a
and 1b. Especially when relatively small scan angles are required, such
as below +/-30 degrees for example, these types of pointing devices have
many disadvantages, or at least a few, among the following list:

[0029] 10. improved RF performance in the case of a reflector
pointing mechanism.

[0030] The above first three (3) points are main advantages when using
rotary actuators.

[0031] According to an aspect of the present invention there is provided
an antenna pointing system for selectively moving a payload relative to a
mounting surface, said system comprising:

[0032] at least one rotary
actuator having a moving part being movable relative to a fixed part
adapted for mounting on the surface;

[0033] a connecting rod movably
connecting to the moving part at a first end thereof and adapted for
movably connecting to the payload at a second end thereof; and

[0034] a
flexible mounting structure for movably attaching the payload to the
mounting surface.

[0035] Conveniently, the flexible mounting structure is a universal joint,
including bearings, flexures or the like, preferably located near a
geometric center of the payload.

[0036] In one embodiment, there are two rotary actuators with essentially
the two second ends of the connecting rods connecting adjacent a
perimeter of the payload, the two actuators being angularly spaced from
one another relative to a rotation center of the flexible mounting
structure, typically by an angle sufficient to make use of the full
angular displacement range of the payload about the flexible mounting
structure.

[0037] In one embodiment, there are first and second rotary actuators
connecting to respective said connecting rod with said second ends of
said connecting rods movably connecting to corresponding first and second
attachment points of the payload.

[0038] Typically, the first and second attachment points are angularly
spaced from one another relative to a rotation center of the flexible
mounting structure, and the first and second attachment points are
substantially adjacent a perimeter of the payload.

[0039] Conveniently, the first and second attachment points are
substantially 90 degrees apart from one another relative to the rotation
center of the flexible mounting structure.

[0040] Other objects and advantages of the present invention will become
apparent from a careful reading of the detailed description provided
herein, within appropriate reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In the annexed drawings, like reference characters indicate like
elements throughout.

[0042] FIGS. 1a and 1b are side and rear elevation views, respectively, of
an antenna reflector mounted with a prior art two-axis gimbal pointing
system;

[0043] FIG. 2 is a top perspective view of an embodiment of an antenna
pointing system in accordance with the present invention movably
supporting an antenna reflector payload;

[0044] FIG. 3 is an enlarged top perspective view of a rotary actuator of
the embodiment of FIG. 2;

[0045] FIG. 4 is a partially broken enlarged top perspective view of a
universal joint of the embodiment of FIG. 2; and

[0046] FIG. 5 is a partially broken top plan view of the embodiment of
FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

[0047] With reference to the annexed drawings the preferred embodiments of
the present invention will be herein described for indicative purpose and
by no means as of limitation.

[0048] Referring to FIGS. 2 and 3, there is shown a schematic diagram of
an embodiment of the low profile high resolution and torque antenna
pointing system 10. In the case presented, the pointing system 10 points
a reflector, part of an RF (Radio Frequency signal) antenna 12 mounted on
board of a spacecraft, represented by the mounting surface 14 situated in
orbit. The pointing system 10 consists of using rotary actuators 20 in
conjunction with cranks 22 and connecting rods 24 to impart rotations to
a payload structure 26, such as an antenna reflector assembly, which is
movably held in place by a flexible mounting structure 28 as a universal
joint structure or the like. An example of the complete system 10 is
shown in FIG. 2.

[0049] In the embodiment 10, the RF performance is improved because the
generally orthogonal first 30 and second 31 rotation axes of the
universal joint 28 intersects a point proximate the geometric center of
the reflector 26, to define the rotation center R thereof. The system 10
uses two rotary actuators 20 to drive two degrees of freedom. Both rotary
actuators 20 have their fixed part secured to the base plate 14
eliminating any mobile harnessing, such as RF rotary joint, electrical
wiring, etc. A crank 22 is assembled on the output of the moving part of
both rotary actuators 20. A rotary actuator 20 with its crank 22 is shown
in FIG. 3.

[0050] An elongated connecting rod 24 has a first proximal end 32 movably
connected to the shaft 23 of the crank 22 and the opposite second distal
end 34 movably connected to the payload 26, at an attachment point 27
typically adjacent a perimeter thereof. Typically, both ends 32, 34 are
connected through spherical bearings 35, flexures or the like in order to
allow angular displacements thereof between respective connecting
elements. The payload 26 is movably mounted on the surface 14 using the
universal joint 28 typically consisting of one to two (1-2) static
brackets 36 securable to the surface 14 and movably supporting a cross 38
about the first rotation axis 30 via at least one first bearing 40,
flexure or the like, and one to two (1-2) moving brackets 42 extending
from or secured to the payload 26 and movably supported by the cross 38
about the second rotation axis 31 via at least one second bearing 44,
flexure or the like, as shown in FIG. 4.

[0051] As best seen in FIG. 5, the two attachment points 27 connecting to
the two second distal ends 34 of the respective connecting rods 24 are
typically angularly spaced from one another relative to the rotation
center R of the flexible mounting structure 28, as illustrated by angle
A. Angle A is typically sufficient to make use of the full angular
displacement range of the payload 26 about the flexible mounting
structure 28. To this end, angle A is preferably around 90 degrees.

[0052] Although the antenna pointing system has been described with a
certain degree of particularity, it is to be understood that the
disclosure has been made by way of example only and that the present
invention is not limited to the features of the embodiments described and
illustrated herein, but includes all variations and modifications within
the scope and spirit of the invention as hereinafter claimed.

Patent applications in class Rotary to or from reciprocating or oscillating

Patent applications in all subclasses Rotary to or from reciprocating or oscillating